Mouse and human natural killer T (NKT) cells recognize a restricted set of glycosphingolipids presented by CD1d molecules, including self iGb3 and microbial alpha-glycuronosylceramides. The importance of the canonical Valpha 14-Jalpha18 TCR alphachain for antigen recognition by NKT cells is well recognized, but the mechanisms underlying the Vbeta8, Vbeta7, and Vbeta2 bias in mouse have not been explored. To study the influences of thymic selection and the constraints of pairing with Valpha 14-Jalpha 18, we have created a population of mature T cells expressing Valpha 14-Jalpha 18 TCRalpha chain in CD1d-deficient mice and studied its recognition properties in vitro and in vivo. Transgenic cells expressed a diverse Vbeta repertoire but their recognition of endogenous ligands and synthetic iGb3 was restricted to the same biased Vbeta repertoire as expressed in natural NKT cells. In contrast, alpha-GalCer, a synthetic homologue of microbial alpha-glycuronosylceramides, was recognized by a broader set of Vbeta chains, including the biased NKT set but also Vbeta6, Vbeta9, Vbeta10, and Vbeta14. These surprising findings demonstrate that, whereas Vbeta8, Vbeta7, and Vbeta2 represent the optimal solution for recognition of endogenous ligand, many Vbeta chains that are potentially useful for the recognition of foreign lipids fail to be selected in the NKT cell repertoire.